A method for transferring graphene grown on CVD onto substrates is known from Suk et al. The method is referred to as a wet transfer and is used widely (Suk, J. W., Kitt, A., Magnuson, C. W., Hao, Y., Ahmed, S., An, J., . . . Ruoff, R. S. (2011). Transfer of CVD-grown monolayer graphene onto arbitrary substrates. ACS Nano, 5(9), 6916-24.). The wet transfer comprises the following steps (FIG. 1—prior art):
a) First, graphene 2 is grown on a copper foil 3 by way of the CVD method [Mattevi, C, Kim, H., & Chhowalla, M. (2011), A review of chemical vapour deposition of graphene on copper, Journal of Materials Chemistry, 21(10), 3324.]
b) The graphene 2 on the copper foil 3 is thereafter spin-coated with a 200 to 500 nm thick PMMA film 1. (FIG. 1a).
c) The film is placed in a copper etching solution 4 with the copper 3 first (FIG. 1b) and is retained there until it is ensured that the copper has completely dissolved. Thereafter, the etching solution is replaced with deionized water 5 so as to clean the PMMA/graphene film 1, 2.d) The target substrate 6 is used as a “fishing” tool to collect the PMMA/graphene film 1, 2 from the water surface 5 (FIG. 1c).e) The substrate 6 is dried, and the PMMA is removed by way of solvent (FIG. 1d). The graphene 2 remains on the target substrate 6 (no reference numeral shown).
Layers having the same hatching in FIGS. 1a to d correspond to one another.
The “fishing transfer” is easy to carry out for substrates extending up to 1 inch. Problems, however, occur at dimensions of 4 to 8 inches. The disadvantage is that the “wet transfer” becomes increasingly difficult to carry out with larger graphene pieces, and too many defects arise due to creases and cracks in the transferred structures on the substrate. Even if a large piece of graphene having a dimension, in inches, of n inches, such as n>2, is successfully transferred onto an n-inch substrate or wafer, the majority of the graphene is generally etched away again after the transfer, which is an uneconomical waste of material.
It is also not possible to transfer more than 2 pieces of graphene with precision onto a desired location on the target substrate, while ensuring an exact distance between the pieces, using the conventional “wet transfer” method. Ultimately, the small graphene pieces move away from the desired location again during drying and fishing, due to the surface tension of the water.